In Deutsche Offenlegungsschrift (DE-OS) No. 26-43-102 there is disclosed a planetary feeding device for electrode wire wherein the adjusting of the wire-feeding rollers is performed by a calibrated spring and the electrode wire fed thereby is subjected to a steady compressing force.
This device consists of a housing on one side of which, running parallel to the passage therethrough for feeding electrode wire, there are seats wherein axially movable pistons are housed. Each piston has a rigidly fixed stub shaft thereon upon which there is mounted by way of a bearing a wire-feeding roller having an outer work surface of hyperbolic shape. The stub shafts upon which the wire-feeding rollers are mounted are disposed perpendicular to the axes of movement of the pistons, and are disposed at an angle of from 20.degree.-45.degree. with respect to each other.
The other side of the housing has an elongated hollow cylindrical part upon which there is mounted an axially movable guiding cone. The movement of the cone is limited by an adjusting nut. The nut is threaded onto the end of the hollow cylindrical part of the housing. Between the guiding cone and the periphery of the housing, on its hollow cylindrical part, there is disposed a calibrated spring. The spring constantly pushes the guiding cone outwardly from the periphery of the housing. Cutouts are machined along the periphery of the housing, double-armed levers having arms of different lengths are hingedly affixed to the housing at the cutouts upon axles. The shorter arm of each lever rests on the head of one of the pistons, while the longer arm cooperates with the outer surface of the guiding cone by means of a roller mounted upon the end of such longer arm.
The double-armed levers are disposed parallel to the electrode wire being fed by the device, and thus the differences in their lengths and in their overall lengths are of considerable importance to the magnitude of the compressive force exerted by the wire-feeding rollers upon the electrode wire. The prior device now being described feeds the electrode wire with a constant forwarding force. It also can be used to work with electrode wires of various diameters.
Such prior device, however, has the very considerable disadvantage that the location of the levers markedly increases its dimensions. The comparatively great lengths of the wire-feeding device, due mainly to the length of the levers, contributes to increased centrifugal forces acting thereupon by reason of its unbalance, thereby shortening the operating life of the bearings of the electric motor which drives it. Another important shortcoming of the above-described prior device is the inability of providing directly an elastic link between the rollers and the resilient element such as the calibrated spring.
The impact of the centrifugal forces when feeding the electrode wire at high speeds is also disadvantageous. In this case, because of the comparatively greater mass of the pistons and rollers plus the mass of the longer arms of the levers, it is difficult to achieve a centrifugal compensation. The centrifugal forces acting at the lower ends of the levers are a resultant of the tangential force produced by the rotation of the device and the radial force resulting from the centrifugal forces developed by the rotating masses. This resultant has not been compensated for in a completely satisfactory manner.
Another known planetary wire-feeding device is shown in Deutsche Offenlegungsschrift (DE-OS) No. 26-43-10. In such latter known device, the disadvantage resulting from the location of the levers parallel to the electrode wire is eliminated, the device employing bow-like levers which are located perpendicularly to the direction of travel of the wire. As in the first-described prior device, the shorter arm of each lever is in contact with pistons which slide the work-feeding rollers, while the longer arms engage the working surfaces of a cam which is rotatable with respect to the housing and is directly driven by the electric motor.
An important disadvantage of such above-described second prior device is the lack of an elastic element to ensure a smooth gradually-increasing force of engagement between the wire-feeding rollers and the wire. Here the compression force is not calibrated; this is not equally desirable in the feeding of wires of different hardnesses, such as hard wires (steel) or soft wires (aluminum). The adjustment of the wire-forwarding force exerted by the feeding rollers is effected by the difference between the masses of the cam and of the housing in their mutual rotation and cannot be changed when working with wires of different degress of hardness.